Metallurgist最新文献

Elevation of the fraction of secondary metallurgical raw materials under the conditions of shortage of high-quality ore feedstock is one of the key challenges for the development and sustainability of nonferrous metallurgy. In connection with the growing volume of motor scrap formed as a result of recycling of the vehicles and military equipment, it seems to be very important to improve the efficiency of its processing aimed at the production of high-quality products made of aluminum-silicon (Al-Si) alloys. The Al-Si alloys (silumins) occupy a special place in modern industry due to their excellent mechanical properties, superior corrosion resistance, and favorable casting characteristics. Hence, they are extensively used in high-standard branches of industry, such as automotive and aerospace engineering, as well as for strategic applications. The present work addresses the main features of innovative technologies aimed at enhancing the quality of secondary AI-Si alloys, including the procedures of electromagnetic stirring combined with directed degassing of the melt aimed at getting thixotropic structures with improved mechanical properties and the minimal number of defects. A modified scheme is proposed for preparing the melt in a rotary furnace with directed degassing in a flow vessel followed by plasma injection and casting into an electromagnetic crystallizer by using specialized molds. A series of melts was carried out with AI-Si alloys with variable chemical compositions. The metallographic analysis of samples was carried out with the help of a scanning electron microscope equipped with a device for energy-dispersive X‑ray spectroscopy. We also studied the surface morphology and the distribution of elemental composition of the samples of alloys. As a result, we obtained castings with uniform thixotropic structures.

This paper presents a novel technology for processing wire made from a microcomposite copper-based alloy. This technology involves deforming the wire in a rotating, equal-channel, angular, stepped matrix, followed by drawing. Deformation of a 6.5 mm diameter wire was conducted in three passes at room temperature, reducing the diameter to 5.0 mm. This treatment resulted in a gradient microstructure featuring an ultradispersed surface layer (grain size ~400 nm) and a gradual increase in grain size toward the center of the wire. Microhardness values were measured at 1150 MPa in the surface zone, 770 MPa in the neutral zone, and 685 MPa in the central zone. The presence of a gradient microstructure, characteristic of deformed materials, is confirmed by the symmetric range of microhardness values observed across the entire cross-section of the rod. Numerous experiments using a combination of traditional and modern research methods substantiate the validity of the results.

In recent years, the problem of recycling and reuse of scrap and wastes of the cable industry has become increasingly urgent. Traditionally, these wastes are treated by high-temperature firing of used electric cables followed by the extraction of the metal core from the processed products. In this connection, it is of interest to study the process of thermal destruction of the cable insulation because it leads to the formation of a volatile fraction containing chlorine compounds, other toxic gases and dust, which worsens the state of the environment and threatens human health. In the present work, we study the general regularities of the kinetics of thermal destruction of the PVC cable insulation both in the initial state and after treatment in liquids (in water and in a solution of acetic acid). We performed systematic investigations of the process of thermal destruction of the samples of PVC insulation within the temperature range 25–600 °C. As the object of investigations, we used samples of PVC cable insulation commercially produced by the Russian cable industry. It was shown that the complete and intense release of the volatile fraction occurs within the indicated temperature range. It was also experimentally established that the kinetic dependence of this process and its constant is quite complicated and described by a kinetic equation of fractional order. As a result of processing of the experimental data, we establish the rates of thermal destruction of the analyzed samples of PVC insulation and the corresponding activation energies of the process. It is also shown that the procedure of holding of PVC insulation samples in acetic acid and in cold water decreases the values of activation energy by more than a factor of 1.13–2.17 as compared with the original PVC insulation samples.

The weldability of X80 strength grade pipes made from 13Cr martensitic stainless steel is studied. Guidelines are proposed for selecting preheating temperatures and post-weld heat treatment conditions.

The necessity of pre-metalizing briquettes for blast furnace production is justified as a means of imparting mechanical strength comparable to that of pellets. The criteria for selecting the roasting metallization method for ore and ore-carbon briquettes are discussed. The proposed approach allows for the production of high-strength lump charge material with a high iron content and significantly reduced binder consumption compared to traditional cold briquetting. Experimental results confirm the possibility of achieving metalized briquettes with strength values that exceed those of roasted pellets. The applicability of the Ryshkowitch–Duckworth model for assessing briquette strength during roasting is also demonstrated. Finally, a comparison is conducted between metallization using roasting furnaces and the Midrex direct ironmaking reactor.

For sheet metal products with a thickness of 2 mm, fabricated using a new non-heat treatable eutectic alloy based on the Al–1Ca–5.5Zn–1.5 Mg system, a weld seam was obtained using friction stir welding. Scanning and transmission electron microscopy, as well as mechanical tests for hardness and uniaxial tension were used to study the fine structure and mechanical properties of the resulting weld seam and near-weld area. Analysis of the weld seam microstructure has revealed a deep refinement of the crystals of the eutectic phase (Al, Zn)₄Ca (average particle size < 5 μm) along with their more uniform distribution across the cross–section in comparison with the base metal. There is a little difference between the structure in the center of the weld and the thermomechanically affected zone. Analysis of the hardness distribution profile in the weld seam cross-section has revealed a slightly higher hardness in the center of the mixing zone (HV117) compared to the base metal (HV110). TEM analysis of the microstructure shows the formation of a recrystallized structure with an average grain size of about 1 μm. Individual inclusions of insoluble Ca-containing crystals measuring less than 100 nm in size are found along the grain boundaries, suggesting their role as boundary migration barriers. The uniaxial tensile tests have shown that the ultimate strength of the weld seam samples is equal to that of the base metal (~330 MPa), leading to a conclusion about the strength factor being close to 1.

This work presents the investigation of the influence of increasing the temperature of the melt and the holding time before refilling the overflow section of the ingot on the behavior of convective flows (descending and ascending) during the solidification of model ingots. The study was conducted using the method of physical (cold) modeling on a flat mold model (mold-crystallizer). A scaled model of a forging ingot weighing 19.6 t was used as an analog. The setup allows for the visualization of processes occurring during the solidification and structure formation of a forging ingot made of calm steel. A pentahydrate solution of sodium thiosulfate (Na₂S₂O₃·5H₂O) was used as the modeling solution. The pouring of the melt into the mold-crystallizer was performed from above. This work is a continuation of previously published studies on the influence of differential pouring technology on the solidification and structure formation processes in forging ingots. The study shows that for all model ingots, the maximum velocity of convective flows is observed at the initial stages of solidification, which is caused by the kinetic impact of the falling stream on the solidifying melt within the ingot. After the pouring of the melt into the ingot body is completed, the velocity of the descending flows rapidly decreases. Refilling the overflow section of the ingot with melt after various time intervals leads to an increase in the velocity of both descending and ascending convective flows. It was established that the maximum increase in the velocity of convective flows occurs when 50% of the solid phase is formed. Further solidification results in a decrease in the descending flows, while the velocity of the ascending flows increases. Increasing the interval between refilling the overflow section with melt to 40 min results in a 1.4-fold increase in the solidification time of the model ingot. It was determined that raising the temperature of the added melt portions leads to a greater difference between the velocities of the ascending and descending flows.

The objective of this study is to determine the feasibility of using experimental equipment in a continuous casting-rolling-pressing process to produce rods from hot-pressed aluminum alloy AD31 scrap. Values of the main temperature-, speed-, and energy-force characteristics were obtained by modeling the process with QForm software. This enabled the determination of the forces acting on the rolls and die, as well as the torques on the rolls and the power of the SPP-200 combined processing unit drive motor. A comparison of these values with the allowable values of the existing equipment revealed that the combined casting-rolling-pressing process can be implemented without overloading the equipment. Additionally, the modeling data can be utilized in designing and assembling the experimental combined processing unit, SPP-200. Experimental studies on producing 9 mm diameter rods from a melt obtained from an electric mixer furnace using scrap profiles of the AD31 alloy were conducted on this unit. The mechanical properties of the rods were determined, and it was found that they meet the requirements of GOST 21488-97 for such products. The energy-force characteristics of the applied unit were measured, and it was determined that the power of its drive motor does not exceed the allowable load.

The effect of aeroacoustic and heat treatments on the structure and mechanical properties of VT1‑0 titanium was studied by comparing welded seam samples before and after the annealing and aeroacoustic treatment. It has been found that a significant change in the structure of titanium caused by the exposure to acoustic fields leads to a more significant decrease in residual stresses compared to annealing, while reducing the level of deforming stress by more than two times during plastic deformation of titanium. Fractographic analysis of the fracture surface of titanium has shown that it undergoes ductile fracture. The titanium structure exhibits a significant number of pits, which grow in size after aeroacoustic treatment.

The basic model for controlling longitudinal thickness deviation has been improved by introducing a graphical solution to a system of two equations, enabling precise adjustment of the longitudinal thickness profile in the finishing stand of a wide-strip cold rolling mill depending on the key process parameters influencing the rolling force. Representing this system with both linear and polynomial equations confirms the validity of the graphical method and facilitates the determination of strip thickness, longitudinal thickness deviation, and the appropriate control actions on the process parameters of the cold rolling process. The improved model was validated by comparing the calculated and measured average values of longitudinal thickness deviation of cold-rolled strips of final thickness on an operating continuous wide-strip mill. The results demonstrate that increasing the front and back specific tensions in the finishing stand reduces longitudinal thickness fluctuations of the rolled strip to within the specified tolerance from the nominal thickness.